The present invention relates to an optical fiber and a dispersion compensator, an optical transmission line and an optical transmission system all of which use this optical fiber and which are applied to e.g., a wavelength division multiplexing (WDM) transmission as one use.
The WDM transmission is a communication system for transmitting signals of plural wavelengths by one optical fiber. In recent years, an erbium doped fiber amplifier (EDFA) using an erbium doped optical fiber is used as an amplifier of an optical signal. This EDFA can directly amplify the optical signal of each wavelength in a wavelength band of 1.5 xcexcm without converting the optical signal to an electric signal in a repeater using the WDM transmission. Therefore, the WDM of optical communication is accelerated by an appearance of the EDFA.
It is well known that a chromatic dispersion and non-linearity obstruct high bit-rate transmission of the optical signal. If the fibers have large chromatic dispersion value, waveform distortion is occurred and no high bit-rate transmission can be performed. On the other hand, when the chromatic dispersion approaches zero, four-wave mixing (FWM) as one of non-linear phenomena is generated and signal distortion is caused so that it is difficult to perform the WDM transmission.
To avoid such a phenomenon, an optical fiber for reducing the non-linearity itself and providing a very small dispersion in a transmission range of the optical signal is proposed in Japanese Patent Laid-Open No. 168046/1995, etc.
The present invention provides an optical fiber suitable for the WDM transmission as one use example, and a dispersion compensator, an optical transmission line and an optical transmission system all of which use this optical fiber. This optical fiber comprises a refractive index profile structure constructed by at least three core layers and a clad outside these core layers;
wherein the three core layers are arranged in an order of first, second and third layers from the inside to the outside;
conditions of 0.8%xe2x89xa6xcex941xe2x89xa63.0%, xe2x88x920.7%xe2x89xa6xcex942xe2x89xa6xe2x88x920.4%, and 0.2%xe2x89xa6xcex943xe2x89xa60.5% are satisfied when a relative refractive index difference of the first core with respect to the clad is set to xcex941, a relative refractive index difference of the second core with respect to the clad is set to xcex942, and a relative refractive index difference of the third core with respect to the clad is set to xcex943;
a cable cutoff wavelength lies on a short wavelength side from 1520 nm; and
the relations of D less than 0, S less than 0, and 0 less than (D/S)xe2x89xa6200 are satisfied in a specific set wavelength band having a range width of not smaller than 20 nm within a wavelength band of 1.5 xcexcm when a chromatic dispersion at a specific wavelength within a wavelength band of 1.5 xcexcm is set to D (ps/nm/km) and a dispersion slope is set to S (ps/nm2/km).